The treatment of cardiac arrhythmias is sometimes performed in conjunction with an ablation catheter inserted into a chamber of the heart or in one of the vessels leading into or from the heart. In the treatment of atrial fibrillation, for example, a radio frequency (RF) ablation catheter equipped with a number of electrodes can be brought into contact with cardiac tissue for creating one or more ablation points along the tissue. During ablation, an RF generator supplies electrical energy to the electrodes. As the RF energy from the tip electrode pass through the contacting tissue to the ground pad, heat is generated in the tissue. The resulting heat from this electric field forms a controlled lesion that blocks the electrical impulses from being conducted through the tissue and serves to promote the normal conduction of electrical impulses through the proper electrical pathway within the heart.
In certain ablation procedures, it may be difficult to electrically isolate the tissue to be treated with a point ablation catheter. In the treatment of paroxysmal atrial fibrillation, for example, it is often tedious and time consuming to isolate the pulmonary veins using an ablation catheter having an ablation electrode that directly contacts the tissue. Moreover, the ablations created by metal ablation electrodes can cause dehydration in the tissue, which can result in scarring and calcification as the lesion heals. Due to the discrete nature of the ablation points, there is also the potential for leaving small gaps of electrically conductive tissue in the ablation line that may continue to initiate points of arrhythmias.